New emissions legislation in Europe and North America is driving the implementation of new exhaust aftertreatment systems, particularly for lean-burn technologies such as compression-ignition (diesel) engines, and stratified-charge spark-ignited engines (usually with direct injection) that are operating under lean and ultra-lean conditions. Lean-burn engines exhibit high levels of nitrogen oxide emissions (NOx), that are difficult to treat in oxygen-rich exhaust environments, which are characteristic of lean-burn combustion. Exhaust aftertreatment technologies are currently being developed that treat NOx under these conditions.
One of these technologies includes a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N2) and water (H2O). This technology is referred to as Selective Catalytic Reduction (SCR). Ammonia is difficult to handle in its pure form in the automotive environment, therefore it is customary with these systems to use a liquid aqueous urea solution, typically at a 32% concentration of urea (CO(NH2)2). The solution is referred to as AUS-32, or diesel exhaust fluid (DEF), and is also known under its commercial name of AdBlue. The DEF is delivered to the hot exhaust stream and is transformed into ammonia in the exhaust after undergoing thermolysis, or thermal decomposition, into ammonia and isocyanic acid (HNCO). The isocyanic acid then undergoes a hydrolysis with the water present in the exhaust and is transformed into ammonia and carbon dioxide (CO2), the ammonia resulting from the thermolysis and the hydrolysis then undergoes a catalyzed reaction with the nitrogen oxides as described previously.
The delivery of the DEF solution to the exhaust involves precise metering of the DEF and proper preparation of the DEF to facilitate the later mixing of the ammonia in the exhaust stream. The delivery of the DEF into the exhaust is typically achieved using some type of injector. In a Reductant Delivery Unit (RDU), the injector is surrounded by a metallic housing. The housing is used to protect the injector, and provide a mounting system to an exhaust pipe and to provide a hydraulic connection interface to the injector. With increased desire for vehicles to be more efficient, and to include more features and capabilities, packaging constraints have become increasingly more restricting.
Accordingly, there exists a need for an injector which allows for greater flexibility with regard to packaging, such that the injector may be mounted in various locations, while adhering to more strict packaging requirements.